Genetics of Neurodegeneration with Brain Iron Accumulation

The condition originally called Hallervorden-Spatz syndrome is a collection of related disorders involving abnormal iron accumulation in the basal ganglia, usually manifesting with a movement disorder. To date, mutations in the following genes have been associated with neurodegeneration with brain iron accumulation (NBIA) phenotypes: PANK2, PLA2G6, FA2H, ATP13A2, C2orf37, CP, and FTL. This collection, now classified under the umbrella term NBIA, continues to evolve as new genes and associated phenotypes are recognized. As this body of information continues to grow, better approaches to diagnosis and treatment have become available. Continued investigations of the underlying pathogenesis of disease, with a focus on lipid, iron, and energy metabolism, will lead to the identification of new therapeutic targets.     

Neurodegeneration with Brain Iron Accumulation: Clinicoradiological Approach to Diagnosis

Discovery of genetic abnormalities associated with neurodegeneration with brain iron accumulation (NBIA) has led to use of a genetic‐based NBIA classification schema. Most NBIA subtypes demonstrate characteristic imaging abnormalities. While clinical diagnosis of NBIA is difficult, analysis of both clinical findings and characteristic imaging abnormalities allows accurate diagnosis of most of the NBIA subtypes. This article reviews recent updates in the genetic, clinical, and imaging findings of NBIA subtypes and provides a practical step‐by‐step clinicoradiological algorithm toward clinical diagnosis of different NBIA subtypes.     

Brain Accumulation of Amyloid-beta in Non-Alzheimer Neurodegeneration

We report an unusual case of amyotrophic lateral sclerosis (ALS) marked by extensive cerebral amyloid-beta deposition in small and medium-size vessels, capillaries, and perivascular plaques in the cerebral cortex, and in most leptomeningeal vessels. Despite considerable cerebral amyloidosis, the patient remained cognitively intact until death. For comparison with other neuro-degenerative diseases and normal aging, we assessed the densities of amyloid-beta-immunoreactive cortical vessels and plaques in matched frontal and temporal lobe sections from archival uncomplicated cases of Alzheimer's disease (N=10), Pick's disease (PkD; N=4), Parkinson's disease (PD; N=6), Diffuse Lewy body disease (DLBD; N=7), progressive supranuclear palsy (PSP; N=5), multiple systems atrophy (MSA; N=4), ALS (N=7), or normal aging (N=10) by semi-quantitative grading (0 to 3+). Moderate (2+) or abundant (3+) cerebrovascular amyloid-beta immunoreactivity was detected in 8/10 AD, 3/7 DLBD, 3/6 PD, 1 each with PSP or PkD, and 2/10 controls. Moderate or abundant densities of amyloid-beta-immunoreactive diffuse plaques were detected in all cases of AD or DLBD, 4/6 with PD, 3/5 with PSP, and 2/10 controls. Moderate or abundant amyloid-beta-immunoreactive mature (dense core) plaques were present in all cases of AD or DLBD, and 3 each with PD or PSP. Importantly, amyloid-beta-immunoreactivity was not observed in the 4 MSA or 7 archival ALS cases. This study demonstrates that prominent amyloid-beta accumulation in cerebral vessels and plaques occurs frequently in AD, DLBD, PSP, and PD, but not in ALS or MSA, indicating that the case described is unique. The lack of cognitive impairment in the case presented argues against the idea that extensive amyloid-beta deposition in the brain causes dementia.     

Subthalamic and pallidal oscillatory activity in patients with Neurodegeneration with Brain Iron Accumulation type I (NBIA-I)

ObjectivesNeurodegeneration with Brain Iron Accumulation type I (NBIA-I) is a rare hereditary neurodegenerative disorder with pallidal degeneration leading to disabling generalized dystonia and parkinsonism. Pallidal or subthalamic deep brain stimulation can partially alleviate motor symptoms. Disease-specific patterns of abnormally enhanced oscillatory neuronal activity recorded from the basal ganglia have been described in patients with movement disorders undergoing deep brain stimulation (DBS). Here we studied oscillatory activity recorded from the internal globus pallidus (GPi) and the subthalamic nucleus (STN) to characterize neuronal activity patterns in NBIA-I.MethodsWe recorded local field potentials (LFP) from DBS electrodes in 6 juvenile patients with NBIA-I who underwent functional neurosurgery. Four patients were implanted in the STN and two patients in the GPi. Recordings were performed during wakeful rest. An FFT-based approach was used to analyze the power spectrum in the target area.ResultsIn all patients we found distinct peaks in the low frequency (7–12 Hz) and in 5 out 6 also in the beta frequency range (15–30 Hz) with the largest beta peak in the patient that presented with the most prominent bradykinesia. No distinct peaks occurred in the gamma frequency range (35–100 Hz). The oscillatory pattern did not differ between STN and GPi.ConclusionsHere we show for the first time the oscillatory activity pattern in the STN and the GPi in juvenile patients with dystonia plus syndrome due to NBIA-I. The low frequency peak we found is in line with previous studies in patients with isolated idiopathic dystonia. In our cohort, the pallidal beta band activity may be related to more severe motor slowing in dystonia plus syndrome such as NBIA-I.SignificanceOur results further support the link between hyperkinetic motor symptoms such as dystonia and enhanced basal ganglia low frequency activity irrespective of the underlying etiology of dystonia.     

Multi-View Ensemble Classification of Brain Connectivity Images for Neurodegeneration Type Discrimination

Brain connectivity analyses using voxels as features are not robust enough for single-patient classification because of the inter-subject anatomical and functional variability. To construct more robust features, voxels can be aggregated into clusters that are maximally coherent across subjects. Moreover, combining multi-modal neuroimaging and multi-view data integration techniques allows generating multiple independent connectivity features for the same patient. Structural and functional connectivity features were extracted from multi-modal MRI images with a clustering technique, and used for the multi-view classification of different phenotypes of neurodegeneration by an ensemble learning method (random forest). Two different multi-view models (intermediate and late data integration) were trained on, and tested for the classification of, individual whole-brain default-mode network (DMN) and fractional anisotropy (FA) maps, from 41 amyotrophic lateral sclerosis (ALS) patients, 37 Parkinson’s disease (PD) patients and 43 healthy control (HC) subjects. Both multi-view data models exhibited ensemble classification accuracies significantly above chance. In ALS patients, multi-view models exhibited the best performances (intermediate: 82.9%, late: 80.5% correct classification) and were more discriminative than each single-view model. In PD patients and controls, multi-view models’ performances were lower (PD: 59.5%, 62.2%; HC: 56.8%, 59.1%) but higher than at least one single-view model. Training the models only on patients, produced more than 85% patients correctly discriminated as ALS or PD type and maximal performances for multi-view models. These results highlight the potentials of mining complementary information from the integration of multiple data views in the classification of connectivity patterns from multi-modal brain images in the study of neurodegenerative diseases.     

Transcriptional Dynamics at Brain Enhancers: from Functional Specialization to Neurodegeneration

Over the last decade, the noncoding part of the genome has been shown to harbour thousands of cis-regulatory elements, such as enhancers, that activate well-defined gene expression programs. Driven by the development of numerous techniques, many of these elements are now identified in multiple tissues and cell types, and their characteristics as well as importance in development and disease are becoming increasingly clear. Here, we provide an overview of the insights that were gained from the analysis of noncoding gene regulatory elements in the brain and describe their potential contribution to cell type specialization, brain function and neurodegenerative disease.     

Transgenic Mice Overexpressing the Divalent Metal Transporter 1 Exhibit Iron Accumulation and Enhanced Parkin Expression in the Brain

Exposure to divalent metals such as iron and manganese is thought to increase the risk for Parkinson’s disease (PD). Under normal circumstances, cellular iron and manganese uptake is regulated by the divalent metal transporter 1 (DMT1). Accordingly, alterations in DMT1 levels may underlie the abnormal accumulation of metal ions and thereby disease pathogenesis. Here, we have generated transgenic mice overexpressing DMT1 under the direction of a mouse prion promoter and demonstrated its robust expression in several regions of the brain. When fed with iron-supplemented diet, DMT1-expressing mice exhibit rather selective accumulation of iron in the substantia nigra, which is the principal region affected in human PD cases, but otherwise appear normal. Alongside this, the expression of Parkin is also enhanced, likely as a neuroprotective response, which may explain the lack of phenotype in these mice. When DMT1 is overexpressed against a Parkin null background, the double-mutant mice similarly resisted a disease phenotype even when fed with iron- or manganese-supplemented diet. However, these mice exhibit greater vulnerability toward 6-hydroxydopamine-induced neurotoxicity. Taken together, our results suggest that iron accumulation alone is not sufficient to cause neurodegeneration and that multiple hits are required to promote PD.     

Protective Function of Nicotinamide Against Ketamine-induced Apoptotic Neurodegeneration in the Infant Rat Brain

During development, anesthetics activate neuroapoptosis and produce damage in the central nervous system that leads to several types of neurological disorders. A single dose of ketamine (40 mg/kg) during synaptogenesis in a 7-day-old rat brain activated the apoptotic cascade and caused extensive neuronal cell death in the forebrain. In this study, we investigated the protective effect of nicotinamide against ketamine-induced apoptotic neurodegeneration. After 4 h, neuronal cell death induced by ketamine was associated with the induction of Bax, release of cytochrome c into the cytosol, and activation of caspase-3. One single dose of 1 mg/g nicotinamide was administered to a developing rat and was found to inhibit ketamine-induced neuroapoptosis by downregulating Bax, inhibiting cytochrome c release from mitochondria into cytosol, and inhibiting the expression of activated caspase-3. TUNEL and immunohistochemical analyses showed that ketamine-induced cell death occurred through apoptosis and that it was inhibited by nicotinamide. Fluoro-Jade-B staining demonstrated an increased number of dead cells in the cortex and thalamus after ketamine treatment; treatment with nicotinamide reduced the number of dead cells in these brain regions. Our findings suggest that nicotinamide attenuated ketamine-induced neuronal cell loss in the developing rat brain and is a promising therapeutic and neuroprotective agent for the treatment of neurodevelopmental disorders.     

Meningeal Lymphatic Vessels:A Drain of the Brain Involved in Neurodegeneration?

正Neurodegenerative diseases include several kinds of neurological disorder that are caused by the progressive death of neurons in different regions of the brain.Such diseases affect millions of people worldwide and impose a heavy health burden on modern societies.However,their pathogenesis remains elusive,and disease-modifying methods are not currently available to prevent,halt,or reverse them[1].A common feature of neurodegenerative diseases is     

Neurodegeneration with brain iron accumulation

Neurodegeneration with brain iron accumulation (NBIA) describes a group of progressive extrapyramidal disorders with radiographic evidence of focal iron accumulation in the brain, usually in the basal ganglia. Patients previously diagnosed with Hallervorden-Spatz syndrome fall into this category. Mutations in the PANK2 gene account for the majority of NBIA cases and cause an autosomal recessive inborn error of coenzyme A metabolism called pantothenate kinase-associated neurodegeneration (PKAN). PKAN is characterized by dystonia and pigmentary retinopathy in children or speech and neuropsychiatric disorders in adults. In addition, a specific pattern on brain MRI, called the eye-of-the-tiger sign, is virtually pathognomonic for the disease. Pantothenate kinase is essential to coenzyme A biosynthesis, and the PANK2 protein is targeted to the mitochondria. Hypotheses of PKAN pathogenesis are based on the predictions of tissue-specific coenzyme A deficiency and the accumulation of cysteine-containing substrates. Identification of the major NBIA gene has led to more accurate clinical delineation of the diseases that comprise this group, a molecular diagnostic test for PKAN, and hypotheses for treatment.     

Tau Accumulation via Reduced Autophagy Mediates GGGGCC Repeat Expansion-Induced Neurodegeneration in Drosophila Model of ALS

Expansions of trinucleotide or hexanucleotide repeats lead to several neurodegenerative disorders, including Huntington disease [caused by expanded CAG repeats (CAGr) in the HTT gene], and amyotrophic lateral sclerosis [ALS, possibly caused by expanded GGGGCC repeats (G4C2r) in the C9ORF72 gene], of which the molecular mechanisms remain unclear. Here, we demonstrated that lowering the Drosophila homologue of tau protein (dtau) significantly rescued in vivo neurodegeneration, motor performance impairments, and the shortened life-span in Drosophila expressing expanded CAGr or expanded G4C2r. Expression of human tau (htau4R) restored the disease-related phenotypes that had been mitigated by the loss of dtau, suggesting an evolutionarily-conserved role of tau in neurodegeneration. We further revealed that G4C2r expression increased tau accumulation by inhibiting autophagosome–lysosome fusion, possibly due to lowering the level of BAG3, a regulator of autophagy and tau. Taken together, our results reveal a novel mechanism by which expanded G4C2r causes neurodegeneration via an evolutionarily-conserved mechanism. Our findings provide novel autophagy-related mechanistic insights into C9ORF72-ALS and possible entry points to disease treatment.Electronic supplementary materialThe online version of this article (10.1007/s12264-020-00518-2) contains supplementary material, which is available to authorized users.     

Brain Iron and Zinc Contents of German Patients with Alzheimer Disease

Our first project aimed to determine the average values of Fe and Zn in normal German human brain (5 individuals, 10 brain parts). Determinations were carried out by instrumental neutron activation analysis in Berlin. Quality control measurements were performed using National Institute of Standard Technology standard reference materials. The present results show non-homogeneous distribution of Fe and Zn in normal human brain. Our second goal was to study the possible elemental concentration changes in German patients with Alzheimer disease (5 subjects, 10 brain regions). Fe and Zn values are found to be significantly changed in some AD brain regions compared to the controls. Another object of this work was to extend the method for the determination of elemental concentration not only in whole brain samples (high fat content) but - applying two types of solvent extraction - in lipid fraction and in brain tissue without lipid.     

Brain Iron Metabolism and Brain Injury Following Subarachnoid Hemorrhage: iCeFISH-Pilot (CSF Iron in SAH)

Introduction

Iron-mediated oxidative damage has been implicated in the genesis of cerebral vasospasm in animal models of SAH. We sought to explore the relationship between levels of non-protein bound iron in cerebrospinal fluid and the development of brain injury in patients with aneurysmal SAH.

Methods

Patients admitted with aneurysmal subarachnoid hemorrhage to a Neurointensive care unit of an academic, tertiary medical center, with Hunt and Hess grades 2–4 requiring ventriculostomy insertion as part of their clinical management were included in this pilot study. Samples of cerebrospinal fluid (CSF) were obtained on days 1, 3, and 5. A fluorometric assay that relies on an oxidation sensitive probe was used to measure unbound iron, and levels of iron-handling proteins were measured by means of enzyme-linked immunosorbent assays. We prospectively collected and recorded demographic, clinical, and radiological data.

Results

A total of 12 patients were included in this analysis. Median Hunt and Hess score on admission was 3.5 (IQR: 1) and median modified Fisher scale score was 4 (IQR: 1). Seven of 12 patients (58 %) developed delayed cerebral ischemia (DCI). Day 5 non-transferrin bound iron (NTBI) (7.88 ± 1 vs. 3.58 ± 0.8, p = 0.02) and mean NTBI (7.39 ± 0.4 vs. 3.34 + 0.4 p = 0.03) were significantly higher in patients who developed DCI. Mean redox-active iron, as well as day 3 levels of redox-active iron correlated with development of angiographic vasospasm in logistic regression analysis (p = 0.02); while mean redox-active iron and lower levels of ceruloplasmin on days 3, 5, and peak concentration were correlated with development of deep cerebral infarcts.

Conclusions

Our preliminary data indicate a causal relationship between unbound iron and brain injury following SAH and suggest a possible protective role for ceruloplasmin in this setting, particularly in the prevention of cerebral ischemia. Further studies are needed to validate these findings and to probe their clinical significance.     

Nutri-epigenetics Ameliorates Blood–Brain Barrier Damage and Neurodegeneration in Hyperhomocysteinemia: Role of Folic Acid

Epigenetic mechanisms underlying nutrition (nutrition epigenetics) are important in understanding human health. Nutritional supplements, for example folic acid, a cofactor in one-carbon metabolism, regulate epigenetic alterations and may play an important role in the maintenance of neuronal integrity. Folic acid also ameliorates hyperhomocysteinemia, which is a consequence of elevated levels of homocysteine. Hyperhomocysteinemia induces oxidative stress that may epigenetically mediate cerebrovascular remodeling and leads to neurodegeneration; however, the mechanisms behind such alterations remain unclear. Therefore, the present study was designed to observe the protective effects of folic acid against hyperhomocysteinemia-induced epigenetic and molecular alterations leading to neurotoxic cascades. To test this hypothesis, we employed 8-weeks-old male wild-type (WT) cystathionine-beta-synthase heterozygote knockout methionine-fed (CBS^+/??+?Met), WT, and CBS^+/??+?Met mice supplemented with folic acid (FA) [WT?+?FA and CBS^+/??+?Met?+?FA, respectively, 0.0057-μg g^?1 day^?1 dose in drinking water/4 weeks]. Hyperhomocysteinemia in CBS^+/??+?Met mouse brain was accompanied by a decrease in methylenetetrahydrofolate reductase and an increase in S-adenosylhomocysteine hydrolase expression, symptoms of oxidative stress, upregulation of DNA methyltransferases, rise in matrix metalloproteinases, a drop in the tissue inhibitors of metalloproteinases, decreased expression of tight junction proteins, increased permeability of the blood–brain barrier, neurodegeneration, and synaptotoxicity. Supplementation of folic acid to CBS^+/??+?Met mouse brain led to a decrease in the homocysteine level and rescued pathogenic and epigenetic alterations, showing its protective efficacy against homocysteine-induced neurotoxicity.     

铁代谢异常与中枢神经系统疾病

由于血脑屏障的存在,脑铁代谢与外周器官不同.铁在脑内代谢的异常可致脑铁沉积或脑内铁缺乏,导致细胞生理功能障碍,引起神经细胞的死亡.目前已经发现阿尔茨海默病、帕金森病、癫、不宁腿综合征的发病机制及疾病的发展与脑铁代谢异常有关.     

Accumulation of Non-Transferrin-Bound Iron by Neurons, Astrocytes, and Microglia

Neurodegenerative conditions such as Alzheimer’s disease, Parkinson’s disease, and hemorrhagic stroke are associated with increased levels of non-transferrin-bound iron (NTBI) in the brain, which can promote Fenton chemistry. While all types of brain cells can take up NTBI, their efficiency of accumulation and capacity to withstand iron-mediated toxicity has not been directly compared. The present study assessed NTBI accumulation in cultures enriched in neurons, astrocytes, or microglia after exposure to ferric ammonium citrate (FAC). Microglia were found to be the most efficient in accumulating iron, followed by astrocytes, and then neurons. Exposure to 100 μM FAC for 24 h increased the specific iron content of cultured neurons, astrocytes, and microglial cells by 30-, 80-, and 100-fold, respectively. All cell types accumulated iron against the concentration gradient, resulting in intracellular iron concentrations that were several orders of magnitude higher than the extracellular iron concentrations. Accumulation of these large amounts of iron did not affect the viability of the cell cultures, indicating a high resistance to iron-mediated toxicity. These findings show that neurons, astrocytes and microglia cultured from neonatal mice all have the capacity to accumulate and safely store large quantities of iron, but that glial cells do this more efficiently than neurons. It is concluded that neurodegenerative conditions involving iron-mediated toxicity may be due to a failure of iron transport or storage mechanisms, rather than to the presence of high levels of NTBI.